However old, Windows 3.x is still being used. Calmira XP 4.0 beta gives the Windows 3.x desktop the WinXP look-and-feel. In this new version an XP taskbar has been added, and even experimental support for long file names. Other things Calmira includes is the XP login screen, and more. And here it is, boys and girls, the obligatory screenshot.

Seems i used a wrong word.
Actually i mean what if you open a VS7.0 file in VS7.1 and save it, you can't open it in VS7.0 without any reasons. And they have changed the project format again in VS8.0(2005). As in any VS versions i worked with.
The project format is xml. It is like
[NewSuperTag]title=be cool[/NewSuperTag]
[File]source/main.cpp[/File]
[File]source/main.h[/File]
The good feature of xml file is two-way compatibility (at least on paper).
If you can't read the tag, ignore it. What is the reason to change the tag names, tag layout, etc?

I agree what sometimes breaking compatibility is required, but not with the every version and even revision of the software.

For example if viewing a pdf file from Acrobat7 on my Acrobat5 viewer it just give me a popup what some of the new features will not be displayed.
I don't use MS Office, but i see others have a lot of troubles with it. Too much for me.

So does MS has a technically-blind engineers or they just want you to upgrade.
Guess youself...